Valve issued a challenge to Left 4 Dead 2 players this week. If 20,000 players unlocked the "Stream Crosser" achievement on Steam, they would release the Dead Air campaign early. Of course, players were up for the challenge and easily surpassed 20,000.

Valve announced on their official Left 4 Dead blog that they will release the Dead Air campaign by July 22nd:

"Since you hit your mark, this means we are going to unlock Dead Air early. We are going to try and release it as early as possible but will release it on July 22nd the latest. It isn’t currently ready for release as we have been working on The Terminal and Finale maps and need to test them more internally."

If "Dead Air" sounds familiar, that is because this campaign is an improved re-release of the Dead Air campaign from the original Left 4 Dead. To stay up to date on the latest Left 4 Dead news, keep an eye on their official blog.

Source: Left 4 Dead Blog